Apparatus and method for measuring the temperature of substrates

ABSTRACT

The invention relates to a device for measuring the temperature of substrates, notably semiconductor wafers. The device comprises at least one radiation sensor for measuring the radiation emitted by the substrate and an element ( 19 ) which restricts the field of vision of the radiation sensor and is positioned between the substrate and the radiation sensor. The substrate temperature can be determined correctly and simply, even if the substrate vibrates or is tilting, owing to the fact that the edges ( 20 ) of the element extend in a straight line. The invention also relates to a corresponding method.

BACKGROUND OF THE INVENTION

The present invention relates to a method and an apparatus for measuringthe temperature of substrates, in particular semiconductor substrates orwafers, with at least one radiation detector for measuring the radiationemitted by the substrate, and an element that restricts the field ofvision of the radiation detector and that is arranged between thesubstrate and the radiation detector. The invention furthermore relatesto an apparatus for measuring an object temperature of an object, withat least one heating apparatus including at least one heating elementfor heating the object by means of electromagnetic radiation, with atleast one first radiation detector that detects the radiation comingfrom the object within a first field of vision.

The invention described in greater detail in the following is usedadvantageously in so-called RTP (rapid thermal processor) systems inwhich wafers undergo thermal processing. RTP systems and the rapidheating process used in these systems are known from publications DE 4437 361 C, DE 4 012 615 C, DE 4 223 133 C, or D 4 41 439 1A, as well asfrom U.S. Pat. Nos. 5,226,732, 5,359,693, and 5,628,564. Additionalrapid heating processes and apparatus are described in the followingpublications: J. Nackos: 2nd International Rapid Thermal Conference, RTP'94. Monterey Calif., Proc. p. 421-428 (1994); Arun K. Nanda, TerrenceJ. Riley, G. Miner et. al.: “Evaluation of Applied Materials RapidThermal Processor Using SEMATECH Metrologies for 0.25 μm TechnologyThermal Applications” Part II, Presentation at the Rapid Thermal andIntegrated Processing Conference MRS Spring Meeting '96, San FranciscoCalif.; Terrence F. Riley, Arun K. Nandam, G. Miner, et. al.:“Evaluation of Applied Materials Rapid Thermal Processor Using SEMATECHMethodologies for 0.25 μm Technology Thermal Applications” Part I, ibid;R. Bremsensdorfer, S. Marcus, and Z. Nenyei: “Patterns RelatedNonuniformities During Rapid Thermal Processing”, presentation at theRapid Thermal and Integrated Processing Conference MRS Spring Meeting'96, San Francisco Calif., and subsequently published document by Z.Nenyei, G. Wein, W. Lerch, C. Grunwald, J. Gelpey, and S. Wallmüller:“RTP Development Requirements”, presented at RTP '97 Conference Sep.3-5, 1997 New Orleans. In all of these methods it is necessary tomeasure the temperature at at least one point or surface section of theobject, substrate, or wafer, or the entire substrate surface during thethermal processing procedure. In general, provided for temperaturemeasurement is at least one radiation detector, for instance a waferpyrometer, that measures the electromagnetic radiation coming from thewafer inside a field of vision that is defined by an optical device, forinstance by a field stop shield or restrictor, that in general is acircular apertured plate. The wafer is heated by the electromagneticradiation (largely thermal or infrared radiation) from heat sources, inparticular from rod lamps that produce longitudinal virtual images onthe wafer. For instance, at wafer temperatures greater than about 600°C., a wafer made of silicon acts like a mirror with reflectivity ofapproximately 30%, so that the mirroring property of the wafer producesvirtual images of the rod lamps or heating device. The following is asimplified discussion of virtual images on the wafer or substrate orobject.

During the temperature measurement, a differentiation is madeessentially between systems heated on one side and systems heated on twosides. Systems heated on one side heat the wafer largely from only oneside. In contrast, the temperature is measured on the other side, forinstance by means of a wafer pyrometer. This determines a radiation thatis largely unaffected by the lamp radiation and that is emitted by thewafer or a substrate, by means of which the substrate temperature iscalculated.

FIG. 10 illustrates a system heated on one side. The substrate 6 isheated by a bank of lamps L arranged on one side of the substrate 6. Theradiation emitted by the object is measured by a wafer pyrometer 8 thatis arranged on the side opposite the bank of lamps.

In the one-sided heating systems it is disadvantageous that the speed atwhich the substrate is heated is limited due to the one-sided heating,whereby in general additional undesired temperature gradients caused bystructures on the substrate surface occur within the substrate, inparticular when the structures are formed or are present on the side ofthe substrate that faces the heat source. Furthermore, as a rule thechamber in which the substrate is processed is highly reflective insystems with one-sided heating. This highly reflective chamber limitsthe rate at which the substrate cools, which is disadvantageous in manyprocesses. An additional disadvantage is that deposits such ascondensation can occur when chamber walls are highly reflective, whichchanges the reflectivity of the walls, causing a temperature drift.

The aforesaid disadvantages can be substantially reduced, and to someextent avoided altogether, in a two-sided heating system such as thatdescribed, for instance, in DE 44 37 361, because in two-sided heatingsystems the substrate is heated from above and from below and thereforein general there is no need for a highly reflective chamber.Furthermore, greater heating speed can be achieved due to the heating onboth sides. Since the substrate is also heated from the back side, whichin general has no structures, the aforesaid temperature inhomegeneitiescaused by structures on the substrate surface can be substantiallyreduced. However, in contrast to the one-sided heating system, whenthere is two-sided heating the radiation measured by the wafer pyrometeris overlaid with an interfering radiation coming from the lamps due tothe reflective properties of the substrate. The light reflected on thesubstrate and coming from the lamps, and the virtual lamp imagesresulting therefrom, appear more or less diffuse for the wafer pyrometerdepending on the roughness of the substrate surface.

FIG. 11 illustrates a two-sided heating system that includes banks oflamps L1 and L2 on both sides of the substrate 6. Also shown are thevirtual images V1 of the bank of lamps L1 occurring on the substrate 6due to reflection. The banks of lamps L1, L2 can be arranged such thattheir virtual images cover those of the other bank of lamps. As can beseen in FIG. 11, the wafer pyrometer, within a field of vision, measuresboth the radiation I_(w) emitted from the wafer and a part of the lampradiation I_(i)r_(i) determined by the reflecting properties of thesubstrate, whereby I_(i) is the lamp intensity of the i^(th) lamp of thebank of lamps L1 and r_(i) is an effective reflection coefficient of thesubstrate associated with lamp i.

If the substrate is made of silicon, when temperatures are less than600° C. the overlay with the interfering radiation occurs both inone-sided heating systems and in two-sided heating systems, sincesilicon is transparent for infrared radiation in this temperature range,and the wafer pyrometer thus also detects a lamp radiation transmittedthrough the substrate.

The wafer pyrometer thus detects a radiation coming from the lamps,transmitted through the wafer, and reflected on the wafer, as well as aradiation emitted by the wafer, whereby the portion of the individualcomponents depends on the coating of the substrate, the substratethickness, and/or the substrate temperature. In order that thetransmitted and reflected intensity of the lamps and their virtualimages do not cause a false measurement result of the pyrometer, a partof the heat radiation of the lamps can be forwarded via a plurality offan-like channels to a lamp pyrometer. The intensity measured in thismanner can be used for correcting the intensity measured by the waferpyrometer. The lamp pyrometer is inserted upstream of an imaging means,preferably a cylindrical lens that largely restricts the field of visionof the lamp pyrometer to a rectangle. The virtual images of the lampsmove relative to the limits of the field of vision of the waferpyrometer due to the vibrations that occur during the thermal processingprocedure and due to thermally caused deformations and tilting of thewafer, so that changes occur in the intensity of the heat radiationmeasured by the wafer pyrometer. In particular this skews the amount oflamp radiation by reflection, which results in an error in thetemperature measurement. If, for instance, during the measurement of theheat radiation with the wafer pyrometer, an apertured plate is used thatrestricts the field of vision between the wafer and the wafer pyrometer,fluctuations in intensity occur due to the round, continuous edge of thelimited field of vision of the wafer pyrometer. This skews themeasurement values for the temperature of the wafer surface.

In the RTP systems cited above, the heating apparatus generally includesa plurality of heating elements, for instance in the form of rod lamps,so that the electromagnetic radiation of each heating element can beindividually adjusted by means of a suitable control apparatus. Not onlydoes the option for the control result in numerous advantages in termsof temperature homogeneity across the wafer surface and flexibility withregard to the heating process, it also results in disadvantages fordetermining the temperature of the substrate or wafer, in particularwhen conventional wafer and lamp pyrometers are used. Thus, as describedabove, elements of the pyrometer, or more generally of the temperaturesensors, that restrict the field of vision can have a negative effect ontemperature measuring accuracy, especially when the intensities of thewafer and lamp pyrometers are compared for measuring the temperature inorder, for instance, to correct the effect of the reflection of the lampradiation on the substrate surface. For example, the vibrations of thesubstrate cited above, for instance, but also possible changes inintensity of individual heating elements in the heating apparatus, caninterfere with the measurement result, in particular when the heatingapparatus does not radiate uniformly in space.

Known from DE 41 14 367 A1 is a pyrometer for contactless temperaturemeasurement of running measurement objects in which a cylindrical lensis provided for bundling the radiation coming from the measurementobject.

Publications JP 5-187922 (A) in Patent Abstract of Japan, Sect. P, Vol.17 (1993), No. 609 (P-1640) and DE-OS 21 50 963 indicate and describecontactless measurement of temperatures of an object, whereby arectangular shield is provided between an optical member and an elementthat receives the radiation.

U.S. Pat. No. 5,061,084 indicates and describes an RTP system in whichtwo pyrometers are provided, which system measures the radiation emittedby the object to be measured and the environment and the radiationemitted by the environment alone.

WO 94/00744 A1 indicates and describes an RTP system in which aradiation measurement device measures the radiation emitted by the waferto determine its temperature, whereby one additional radiation measuringdevice is provided that measures the radiation emitted by the lamps.

U.S. Pat. No. 5,841,110 describes an RTP system in which two pyrometersare provided for measuring the wafer temperature and the ambienttemperature or lamp temperature.

The object of the invention is to suggest and provide a method and anapparatus for measuring the temperature of substrates, with which methodand/or apparatus it is possible to correctly and simply determine thesubstrate temperature, even when the substrate vibrates or tilts.

SUMMARY OF THE INVENTION

Starting with an apparatus known from DE-OS 41 14 367 for measuring thetemperature of substrates, in particular semiconductor wafers, with atleast one radiation detector for measuring the radiation emitted by thesubstrate, and a restrictor that restricts the field of vision of theradiation detector and that is arranged between the substrate and theradiation detector, whereby the edges of the restrictor are essentiallystraight lines, this object is inventively achieved in that therestrictor is a polygonal restrictor.

The limitation in the field of vision that is achieved in this manner inthe radiation detector for measuring the radiation emitted by thesubstrate, for instance in a pyrometer, offers the advantage over thepreviously known circular restriction in the field of vision using anapertured plate that the field of vision is restricted by a polygonalrestrictor so that the pyrometer, hereinafter also referred to as thewafer pyrometer, measures a constant intensity of the heat radiationreflected by the wafer despite any vibrations or tilting in thesubstrate when the migration of the virtual lamp images caused byvibrations or tilting is not greater than the boundary lines of apolygonal stage or step that is perpendicular to the lamp images.

The polygonal restrictor produces a polygonally restricted, multistagefield of vision of the wafer pyrometer. In contrast, a rectangular fieldof vision is created in the case of the rectangular shield, and alargely rectangular field of vision is created in the case of thecylindrical lens.

Preferably the wafer is heated by heat sources such as, for instance,lamps. The heat sources are preferably longitudinally extended heatingelements. Virtual images of these heating elements are created by thewafer so that, as with a mirror, longitudinally extended virtual imagesof the heating elements are produced by the wafer.

The restriction in the field of vision of the wafer pyrometer shouldoccur in general such that the lamp images intersect at right angles theboundary lines of the field of vision of the wafer pyrometer. Due to thestraight-line restriction of the field of vision, the radiation fallingon the wafer pyrometer does not change when the wafer vibrates or tilts.In conventional round shields, a change in the light intensity fallingon the wafer pyrometer would occur if the wafer vibrated or tilted.

In order to eliminate the lamp radiation from the intensity determinedby the wafer pyrometer, the heat radiation of the lamps is forwarded,for instance in a fan-like manner, via a plurality of channels to anadditional radiation detector, preferably a pyrometer, and the intensitythus measured is used for correcting the intensity measured by the waferpyrometer. This radiation detector is hereinafter referred to as a lamppyrometer. An imaging means, preferably a cylindrical lens, whichrestricts the field of vision of the lamp pyrometer to a largelyrectangular shape, can be inserted upstream of the lamp pyrometer.

It is also possible to provide a plurality of wafer pyrometers that alsomeasure the wafer radiation overlaid by the lamp radiation. Likewise, aplurality of lamp pyrometers can be provided.

For determining the substrate or object temperature, the measuredintensity of the wafer pyrometer is compared to the measured intensityof the lamp pyrometer. This is not possible with a circular restrictionin the field of vision of the wafer pyrometer using an apertured plate,in particular when wafer vibrations occur, because the intensitymeasured by the wafer pyrometer also fluctuates due to the aperturedplate.

In one advantageous embodiment of the invention, an optical system, forinstance a lens system, is located between the wafer and the waferpyrometer, which system produces on the wafer pyrometer an optical imageof the wafer surface restricted by the element. The restrictor islocated preferably in the intermediate image plane of this lens system.

Preferably a device for rotating the wafer is provided for the inventiveapparatus in order to heat the wafer surface uniformly.

In addition, the inventive apparatus can have not only one, but also aplurality of wafer pyrometers. The rectangular fields of vision of thesewafer pyrometers are preferably parallel so that equivalent images ofcircumferential segments of the wafer surface are always formed on thewafer pyrometer when a wafer is rotated. Boundary lines of therectangular fields of vision are then intersected at right angles by thelamp images. Since the wafer is being rotated, the parallel arrangementof the rectangular fields of vision is only required on a half-plane ofthe wafer. The fan of the lamp pyrometer is arranged in a correspondingmanner so that again the intensity of the lamps can be clearlyassociated with the intensity of the rectangularly-restricted wafersurface. In this arrangement, it is sufficient to have a single lamppyrometer that is allocated to the field of vision of at least one ofthe wafer pyrometers, provided the intensity is approximately constantacross the length of the coil within a lamp.

The object is furthermore achieved by a method in which the field ofvision of the wafer pyrometer is restricted in straight lines by theelement between the wafer and the wafer pyrometer.

Because of the straight-lined restriction of the field of vision, theradiation falling on the wafer pyrometer does not change when the wafervibrates or tilts. In conventional round shields, there would be achange in the light intensity falling on the wafer pyrometer when thewafer vibrated or tilted.

In accordance with one advantageous embodiment of the invention, thewafer is heated by at least one heat source spaced from the wafer. Sincethe radiation falling on the wafer from the heat source is reflected ina different direction when the wafer vibrates or tilts, when there is astraight-lined restriction in the field of vision there is thus nochange in the radiation intensity for the radiation falling on the waferpyrometer.

In one exemplary embodiment in which an optical imaging system, forinstance a lens system, is located between the wafer and the waferpyrometer and creates optical images on the wafer pyrometer of the wafersurface restricted by the element, the radiation falling on the waferpyrometer from the wafer is restricted in straight lines by the image ofthe element, the advantages cited in the foregoing again being achieved.

In accordance with one additional advantageous embodiment of the method,the wafer is rotated during the radiation process by a rotationapparatus in order to achieve a temperature change in the wafer that isas uniform as possible and a temperature distribution across the wafersurfaces that is as uniform as possible. In this case it is advantageouswhen a plurality of wafer pyrometers and associated elements thatlinearly restrict the field of vision of the wafer pyrometer areprovided that can lie parallel to one another.

One additional object of the invention is to provide an apparatus formeasuring the temperature of substrates, hereinafter also calledobjects, in which the temperature determination is largely independentof changes in intensity in the heating apparatus and/or its virtualimages, or that, in a second embodiment of the invention, fordetermining correction parameters, the electromagnetic radiation thatreaches the first field of vision from at least one heating element isdetected by a measuring apparatus up to an intensity-dependent function.

This object is achieved with an apparatus for measuring an objecttemperature of an object with at least one heating apparatus includingat least one heating element for heating the object by means ofelectromagnetic radiation, with at least one first radiation detectorthat detects the radiation coming from the object within a first fieldof vision, whereby for determining correction parameters of a measuringapparatus the electromagnetic radiation reaching the first field ofvision from at least one heating element is detected up to anintensity-dependent function. This solution is hereinafter referred toas the second embodiment of the invention.

In accordance with the second embodiment of the invention, it isadvantageous that changes in intensity (both in terms of space and interms of time) of the heating apparatus and/or its virtual images (forinstance due to wafer vibrations) do not affect the temperaturemeasurement of the object. This is because the measured intensitiesexperience the same relative changes from the heating apparatus as fromits virtual images, and these are therefore synchronously detected bothby the first radiation detector and by the measurement apparatus. Thismeans that, for instance by finding ratios of intensity values, theeffects of changes in intensity (both in terms of space and in terms oftime) can be compensated in the temperature measurement. It isadvantageous when the intensity-dependent function, which also includesan intensity-independent proportionality factor, is approximately equalfor each heating element.

The measurement apparatus can include an impedance measurement of theheating elements in order to determine the intensity emitted by theheating elements via an impedance/intensity relation. Alternatively oradditionally, thermocouples can be employed for measuring thetemperature of the heating elements in order to determine the emittedintensity of the heating elements via an impedance/intensity relation.

Furthermore, the measurement apparatus can also include a secondradiation detector, whereby the second radiation detector advantageouslydetects the radiation emitted by the heating elements within a secondfield of vision that also determines the intensity-dependent function orproportionality factor, whereby assuming an object acting as a mirrorfor the electromagnetic radiation, the first and the second fields ofvision are almost identical in at least one physical dimension. Ingeneral the type of coincidence between the fields of vision of thefirst radiation detector(s) and second radiation detector(s) can beadapted to the geometry of the heat source or heating elements of theheat source.

It can furthermore be advantageous to measure the radiation coming fromthe object using a plurality of radiation detectors (second radiationdetectors), whereby the fields of vision with respect to the objectsurface are limited to various surface regions of the object, and theirfields of vision are approximately equal in at least one physicaldimension to that of the field of vision of the second radiationdetector. Analogously, a plurality of radiation detectors (firstradiation detectors) can also be used for measuring the radiationemitted by the heating apparatus, for instance the individual heatingelements.

A plurality of radiation detectors for measuring the radiation comingfrom the object is particularly advantageous when the object isrotatable by means of a rotation apparatus. Then surface regions of theobject can be detected at different radial distances due to thearrangement of the second radiation detectors relative to the axis ofrotation of the rotation apparatus, which makes it possible to acquire aradial temperature profile. It is this site-selective temperaturedetermination of the object that makes it possible to adjust a radialtemperature profile that is regulatable in wide limits across the wafersby controlling the heating elements of the heating apparatus, forinstance of rod-shaped lamps, in particular halogen or arc lamps. It isadvantageous when the electromagnetic radiation of each heating elementis individually adjustable via a control apparatus.

Since for example temperature deviations from the target values of a 300mm wafer at a mean wafer temperature of 1000° C. must, for example, beless than 2° C., it is necessary for the radiation detectors to detectthe electromagnetic radiation with nearly absolute accuracy. This ismade reliably possible by the described embodiments of the presentinvention.

It is furthermore advantageous when the fields of vision of theradiation detectors are adapted to the symmetry of the heating elements.Thus, for instance when rod-shaped heating elements are used, arectangular field of vision, for instance, can be defined by suitablemeans such as restrictors and/or an optical imaging system comprisinglenses, Fressnel lenses and/or zone plates. If the heating apparatuscomprises rod-shaped heating elements arranged parallel to one another,the fields of vision of the radiation detectors are advantageouslylargely determined by cylindrical lenses arranged coaxially to theheating elements. This has the advantage that a field of vision opensperpendicular to the cylindrical lens axis, wherein the reflectivity ofthe object, which is integrated over a large angle, can be determined.Furthermore the determination of intensity using such fields of visionis not sensitive to vibrations in the object (wafer). In general therestriction of the fields of vision can be arranged such that, assumingan object that is reflective for the electromagnetic radiation of theheating apparatus, a minor displacement of a field of vision and theheating element relative to one another does not significantly affectthe intensity measured by the radiation detectors. How this design isarrived at depends in general on the geometry of the heating apparatusand/or heating elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following using preferred embodimentswith reference to FIGS. 1 through 12. In the drawings:

FIG. 1 is a cross-section through a device for the thermal processing ofwafers for explaining the manner in which the inventive apparatusfunctions in accordance with a first embodiment of the invention;

FIG. 2 is a section along line II—II in FIG. 1;

FIG. 3 is a schematic drawing of a lens system that can be employed inconnection with the inventive apparatus;

FIG. 4 is one exemplary embodiment for an element restricting the fieldof vision of the wafer pyrometer in the form of a polygonal shield orrestrictor;

FIG. 5 is a schematic drawing for explaining the manner in which theinventive apparatus functions;

FIG. 6 is another embodiment of an element restricting the field ofvision of the wafer pyrometer;

FIG. 7 is a drawing of an embodiment with a plurality of waferpyrometers;

FIG. 8 is a schematic drawing of a heating apparatus with rod-shapedlamps arranged parallel to one another, and the virtual heat source,with the virtual lamp images, that results from the reflective effect ofthe object;

FIG. 9 is a top view of a schematic drawing with a plurality of waferpyrometers, the field of vision of which is largely determined bycylindrical lenses arranged coaxial to the rod-shaped lamps of theheating apparatus;

FIG. 10 is a schematic drawing of an RTP system with one-sided heating,in accordance with the prior art;

FIG. 11 is a schematic drawing of an RTP system with two-sided heating,in accordance with prior art; and,

FIG. 12 is a schematic drawing of an RTP system that is heated on twosides and that has a wafer pyrometer and a lamp pyrometer.

DESCRIPTION OF PREFERRED EMBODIMENTS

The rapid heating oven illustrated in FIGS. 1 and 2 has a housing 1, tothe upper and lower interior wall of which are attached banks of lamps4, 5 comprising a plurality of individual lamps or individual lamp tubes2, 3, which heat a semiconductor wafer 6 that is arranged in a reactionchamber 7 between the banks of lamps 4, 5 in the housing 1.

Advantageously the reaction chamber 7 essentially comprises a materialthat is largely transparent for the lamp radiation, which material isalso transparent with regard to the measuring wavelengths or measuringwavelength spectra of the pyrometers or the radiation detectors used.Using silica glass and/or sapphire, which have an absorption coefficientof approximately 0.1 1/cm to 0.001 1/cm determined via the lamp spectra,reaction chambers that are suitable for rapid heating systems can bebuilt in which the thickness of the reaction chamber wall can be between1 mm and several centimeters. The material can be selected in terms ofthe absorption coefficient depending on the thickness of the reactionchamber wall.

Chamber wall thicknesses that measure in centimeters are particularlyrequired when an underpressure, if necessary all the way to a an ultrahigh vacuum, or an overpressure is to be produced in the reactionchamber 7. If the diameter of the reaction chamber is approximately 300mm, for instance, the chamber 7 has sufficient mechanical stability witha silica glass thickness of approx. 12 mm to 20 mm so that the chambercan be evacuated. The thickness of the reaction chamber wall 7 isdimensioned in conformity with the wall material, the chamber size, andthe pressure loads.

Preferably used for lamps are halogen lamps whose filament structure ishelical, at least in part. A partially helical structure makes itpossible advantageously to achieve certain pre-defined geometric andspectral radiation profiles of the lamp. The lamp filament can include,for instance, alternating helical and non-helical filament segments.Both the geometric and the spectral radiation profiles in this case arelargely determined by the distance between adjacent helical filamentsegments. Another option for defining the lamp radiation profile is, forinstance, to vary the thickness of the filament structure, the helixthickness, along the filament.

If the lamp profile is to be controllable, lamps with a plurality ofindividually controllable filaments, preferably rod lamps, can beemployed. Lamps with a controllable lamp profile are particularlyadvantageous in rapid heating systems for heat processing oflarge-surface substrates, such as, for instance, 300 mm semiconductorwafers, since a very homogeneous temperature profile can be obtainedalong the substrate surface using these lamps and a suitable lampcontrol apparatus. Superimposing the individual radiation profiles ofthe filaments results in an overall radiation profile of the lamp thatcan be adjusted in broad ranges. In the simplest case, a halogen lamp,for instance, includes two filaments, each with a helical structure orat least a partially helical structure, for instance, whereby the helixthickness and/or the distance of the helical filament segments of thefirst filament from the first end to the second end of the lampincreases, and the helical thickness and/or distance from the helicalfilament segments of the second filament decreases inversely from thefirst to the second end of the lamp. The overall radiation profile canthus be varied in broad ranges by the selection of the current strengthin the two filaments. Another embodiment option for a lamp withcontrollable radiation profile is that the filament of the lamp includesat least three electrical terminals, whereby different operatingvoltages are applied between each of the terminals. This permits controlof the filament temperature, by segment, and thus of the radiationcharacteristics of the lamp along the filament.

Alternatively to the lamps described in the foregoing, plasma or arclamps can also be employed, whereby the radiation profile is adjustablein this case, as well. Thus, for instance, the lamp spectrum can beadjusted via the current density from the UV range down nearly toinfrared.

As can be seen in FIG. 1, a wafer pyrometer 8 that is arranged on thebottom side of the housing 1 measures, via a small opening 9, which ispreferably but not necessarily formed in a housing wall in the center ofthe wafer 6 to be processed, the electromagnetic radiation that isemitted and reflected by the wafer 6. In addition, in the case ofsilicon wafers, transmitted light is also measured at temperatures below600° C. However, it is also possible to employ a plurality of pyrometersarranged parallel to the wafer surface, as is illustrated in FIGS. 7 and9 and as is described in the following.

Apparatus of the type described in the foregoing are described, forinstance, in Applicant's DE 197 37 802 A, DE 197 54 385 A, and DE 197 54386 A, not previously published, which are referenced here to avoidrepetition and which are included in the content of the presentapplication.

Arranged on the bottom side of the rapid heating oven is an opticalradiation measuring apparatus that includes a pyrometer 10 and, as shownin FIG. 2, a channel body 11 in which radiation channels 12 are formedor milled in the shape of a fan. This pyrometer 10 measures theintensity of the electromagnetic radiation that is emitted by the lampsonto the wafer. Arranged on the side of the channel body 11 facing awayfrom the bank of lamps is a lens system 14, preferably a cylindricallens, such that its focal line is located at or in the vicinity of asite at which the axes of the radiation channels 13 intersect such thatthe radiation falling on the lens system 14 reaches the pyrometer 10. Ascan best be seen in FIG. 2, the radiation channels 12 in the channelbody 11 are embodied or arranged such that the coil 15 of eachindividual lamp 3 lies on the extended longitudinal axis 16 of eachradiation channel 12. The radiation sources and/or the radiationchannels are preferably arranged such that the lamp pyrometer signalresults from a lamp or filament segment that is free of filamentretention apparatus or other means that would have a negative effect onthe flow of radiation or on the temperature of the filament or lampsegment observed through the radiation channels. The pyrometer 10 or itssystem of lenses 14 therefore “looks” precisely at each lamp coil 15,wherein background radiation, which does not come from the lamp coil 15,if it comes at all, makes up only a negligibly small portion of all ofthe light falling on the pyrometer 10, hereinafter also referred to asthe lamp pyrometer. The background radiation can be deliberately maskedusing additional shields or coverings in the vicinity of the lamp coilsand the radiation channels.

FIG. 3 illustrates a lens system 17 that is located between the wafer 6and the wafer pyrometer 8 and that creates an image of the wafer surfacerestricted by a shield or restrictor 18 on the wafer pyrometer 8. Therestrictor 18 is preferably located in the intermediate image plane ofthe lens system 17.

A polygonal restrictor 19 or rectangular restrictor is used for therestrictor, as illustrated in FIG. 4. The length of the straight-linedlimit of one polygon stage or step 20 should be at least as long as thedistance the lamp images 21 drift due to vibrations or tilts of thewafer 6. The arrow 23 is an exemplary illustration of the drifting ofthe lamp images 21 from the position 22 prior to tilting or vibrating tothe position 22′ after such tilting or vibrating. Based on the inventivemeasure of arranging the edges of the restrictor largely in a straightline to the direction of movement of the reflected image, no changes inintensity are caused by the tilting of the wafer pyrometer, in contrastto restrictors with curved edges, for instance apertured plates orelliptically shaped restrictors in which the intensity falling on thewafer pyrometer is a function of the positional displacement orvibration.

FIG. 5 demonstrates the size of the polygonal restrictor 19 compared tothe previously used apertured plate 24. As can be seen from this figure,the surface area of the polygonal restrictor 19, which is integrated inthe radiation measurement using the wafer pyrometer 8, is preferably thesame as the corresponding integration surface area of the aperturedplate 24 used in the past. This also applies to an elliptically shaped“apertured plate” and correspondingly to the rectangular restrictor.

FIG. 6 illustrates another embodiment of a restrictor with polygonallimits. In this example, a quarter of a circle is used as a restrictor,the boundary lines of which are polygon stages rather than the normalstraight lines.

A largely rectangular boundary of the field of vision of the waferpyrometer 8 is also achieved in that a cylindrical lens 14 is positionedin front of the wafer pyrometer 8 rather than the rectangular restrictorlocated in the intermediate image of the lens system 17.

All of the embodiments of the element that restricts the field of visionof the wafer pyrometer 8 are designed such that the boundary lines ofthe field of vision are straight lines or, in the case of thecylindrical lens, are largely straight lines, whereby boundary lines ofthe field of vision preferably intersect the lamp images 21 largely atright angles in order to achieve the advantages of the invention citedin the foregoing.

An additional advantageous embodiment of the invention can be achievedin that a plurality of wafer pyrometers 8 with fields of vision that areparallel to one another are used in the inventive apparatus. FIG. 7illustrates this situation. Again, the lamp images 21 intersect at rightangles boundary lines of the fields of vision, in this instance, of theplurality of wafer pyrometers 8. In addition, the wafer 6 can be rotatedduring thermal processing and temperature measurement, as indicated bythe arrow 25 in FIG. 7. It is sufficient to provide the fields of visionlying parallel to one another on only one half-plane if the wafer isrotated. In this arrangement, a single lamp pyrometer 10 is sufficient;it is allocated to the field of vision of one of the wafer pyrometersprovided the intensity is constant across the length of the coil withinone lamp.

FIG. 8 is a drawing of a heating apparatus 4 comprising one bank oflamps with rod-shaped lamps L1 through L10 arranged parallel to oneanother. Arranged at a distance to the bank of lamps 4 is a wafer or anobject 6 that partially reflects the electromagnetic radiation emittedby the bank of lamps and that is heated by this electromagneticradiation. Likewise shown is a wafer pyrometer or a second radiationdetector 8 that detects the radiation coming from the object. Thisradiation essentially constitutes the radiation emitted by the objectand the reflected portion of the lamp radiation. In practice thisreflection portion is approximately 30% for temperatures greater than6000° C. when using a silicon wafer. The virtual reflected images of thelamps L1 through L10 are likewise illustrated as V1 through V10 andconstitute the virtual bank of lamps 4′. The wafer pyrometer 8 has afield of vision pre-determined by an angle β (first field of vision) andreceives electromagnetic radiation that lies within this field ofvision.

FIG. 8 illustrates another pyrometer, or a second radiation detector 10,that measures the radiation emitted directly by the lamps L1 through L10of the heating apparatus 4. The radiation travels to the detector 10preferably by means of the channel body 11 illustrated in FIG. 2. Thepyrometer 10 also has a field of vision pre-determined by an angle α(second field of vision) that defines the number of lamps observed.

In order to measure the temperature of the object as precisely aspossible, corresponding to the second embodiment of the presentinvention, the first and the second fields of vision of the lamppyrometer 10 and the wafer pyrometer 8 are selected such that they areidentical, at least in terms of physical dimensions, assuming an object6 that reflects the electromagnetic radiation. In the exampleillustrated in FIG. 8, this means that essentially the same segment ofthe virtual reflected image 4′ of the bank of lamps 4 is detected by thewafer pyrometer that corresponds to the segment of the heating apparatus4 that is detected by the lamp pyrometer 10. If, as in FIG. 8, the lampsare rod shaped and emit radiation largely homogeneously in the axialdirection, it is sufficient when the segments of the images detected bythe lamp and wafer pyrometers 10, 8 are approximately the same in thedirection perpendicular to the axes of the lamps. This can be achievedby arranging the pyrometers appropriately, e.g., equivalent angles α andβ.

Advantageously the fields of vision of the pyrometers 8, 10 in theillustrated example are essentially established using cylindrical lenseswhose focal lines run parallel to the rod-shaped lamps L1 through L10.These cylindrical lenses or another suitable imaging means, or theaddition of restrictors, make it possible to establish the apertureangles α and β. If the radiation intensity of the lamps along the lampaxis is approximately constant (which is true in general for onefilament segment), cylinder lenses with different focal line lengths canbe used for the pyrometers 8, 10, since, as described in the foregoing,it is sufficient when the fields of vision of the pyrometers 8 and 10are approximately equal, at least in terms of physical dimensions, inthe direction perpendicular to the lamp axis. This ensures that both thephysical changes and changes over time in the intensities of the lampsand the virtual lamp images are detected synchronously, both by thewafer pyrometer and by the lamp pyrometer, down to a proportionalityfactor.

According to the present invention, in addition to the aforesaid anglesα and β, for instance, which define a plane perpendicular to thedirection of the lamp axis, alternatively or in addition thereto theopening angles of the wafer pyrometer and lamp pyrometer can also beselected approximately equal, that is, for instance, in the direction ofthe axis of the cylindrical lenses. This depends largely on how constantthe lamp intensity is along the lamp axis and on the measuring accuracyrequired for the object temperature.

FIG. 9 is a schematic drawing of a top view of a wafer 6 and a bank oflamps 4 with rod-shaped lamps L1 through L7 that are arranged parallelto one another. The wafer can be rotated about the axis A by a rotationmechanism. FIG. 9 illustrates the application of a plurality of waferpyrometers, each provided with cylindrical lenses Z1 through Z7. Theaxes of the cylindrical lenses are oriented parallel to the lamp axes,wherein the wafer temperature can be detected radially, similar to FIG.7.

In contrast to FIG. 7, the wafer pyrometers in accordance with FIG. 9are arranged along the diameter of the wafer, whereby when there is anasymmetrical arrangement with regard to the axis of rotation theadvantage results that even for wafers with small diameters the radialtemperature profile can be measured at a sufficient number of siteswithout making the axial length of the cylindrical lenses too small.

With a regulating apparatus, a bank of lamps can be controlled by meansof the radial temperature profile, whereby it is advantageous when eachindividual lamp can be individually controlled. This permits atemperature distribution across the wafer to be achieved that is asuniform as possible. It should be mentioned again that in particularwith individual lamp control the equivalence of the fields of vision(precisely identical down to an intensity-dependent function or aproportionality factor) of wafer and lamp pyrometers is a necessaryrequirement for a high degree of measuring accuracy since this is theonly way that the intensity reflected by the wafer can be correctedproperly.

In accordance with the second embodiment of the invention, equivalenceof, the fields of vision should be taken to mean that the fields ofvision of the wafer and lamp pyrometers are nearly identical in thedirection of inhomogeneous intensity distributions of the heatingapparatus down to a proportionality factor (that can also be 1) or ingeneral down to a known intensity-dependent function. In general thefields of vision are, advantageously adapted to the symmetry of theradiation characteristics of the heating apparatus. This can occur, forinstance, due to the selection of suitable field of vision restrictor orimaging means, such as, for instance, a polygonal restrictorcorresponding to the first embodiment of the invention or, for instance,a cylindrical lens. This means, for instance, that it can be achievedthat the intensity measured by the radiation detectors is largelyunaffected when there is a slight displacement of the fields of visionand the heating elements relative to one another. The term heatingelements also includes any virtual images of the heating apparatus thatoccur due to a partial reflection on the object.

As FIG. 12 clarifies, in accordance with the second embodiment of theinvention, in general the second radiation detector (the lamp pyrometer)can be replaced by a measuring apparatus M that detects theelectromagnetic radiation I1 _(i) from the heating elements L1 _(i) ofthe heat source L1, preferably the electromagnetic radiation from eachheating element L1 _(i), that reaches the first field of vision of theradiation detector 8 down to a proportionality factor or a knownintensity-dependent function. Due to the reflecting properties of theobject (for instance, wafer) 6, the radiation detector 8, in addition tomeasuring radiation I_(em) emitted by the object 6 into the first fieldof vision, also measures a radiation I1 _(i)*r_(i) reflected by eachheating element L1 _(i) of the bank of lamps L1, which seems to beemitted from its virtual images V1 _(i). r_(i) is an effectivereflection coefficient relative to the heating element L1 _(i).

The radiation detector 8 thus measures overall the intensityI_(total)=I_(em)+ΣI1 _(i)*r_(i). It is assumed as a simplification thatthe object 6 is opaque for the radiation of the upper bank of lamps L2(the virtual image of which is not illustrated).

For determining the intensity I_(em) emitted by the wafer, therefore, areflective portion ΣI1 _(i)*r_(i) must be corrected. The measuringapparatus M in general measures the intensity I_(M)=c_(i)*I1 _(i) for aheating element L1 _(i), whereby c_(i) is a constant predetermined bythe measuring apparatus or is a known intensity dependent function thatcan be determined, for instance, in a calibration process.

The measuring apparatus M can include, for instance, an impedancemeasurement of the heating element, preferably the lamp filaments, orthe filament temperature of the lamps, for instance, can be determinedby suitable attached thermocouples, whereby the functions or constantsc_(i) are then measured, for instance via impedance/intensity ratios ortemperature/intensity ratios.

In accordance with the invention, c_(i)*I1 _(i)=k_(i)*I1 _(i)*r_(i),whereby k_(i) is an intensity-dependent function associated with theheating element L1 _(i) or is a proportionality factor. Preferably themeasuring apparatus is selected such that the k₁ for all heatingelements L1 _(i) are approximately equal (allowing for measuringerrors), which makes the calibration process in particular substantiallysimpler. For instance, with the embodiment illustrated in FIG. 8, thiscan be achieved with α=β. Thus, when c_(i)/k_(i) or c_(i) and k_(i) areknown, the reflection portion of the intensity detected by the radiationdetector 8 can be corrected using the measuring apparatus and thetemperature of the object can then be measured using the intensityI_(em) emitted by the wafer.

In order to increase the accuracy of the object temperature evenfurther, the first and second embodiments of the invention can beadvantageously combined with one another.

The invention has been described using preferred exemplary embodiments.However, one skilled in the art will be able to find numerousmodifications and embodiments without departing from the inventiveconcept.

The specification incorporates by reference the disclosure of Germanpriority documents 199 05 524.6 of 10 Feb. 1999 and PCT/EP00/00375 of 19Jan. 2000.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

1. An apparatus for measuring the temperature of substrates, comprising:at least one first radiation detector for measuring radiation emitted bysaid substrate; at least one elongated heating element for heating saidsubstrate: a polygonal restrictor that restricts a field of vision ofsaid at least one first radiation detector, wherein said restrictor isdisposed between said substrate and said at least one first radiationdetector, wherein edges of said restrictor defining said field of visionare essentially linear and stepped, wherein images of said elongatedheating element on said substrate intersect, at substantially rightangles, boundary lines forming a polygon step of said field of vision,and wherein ones of said boundary lines extending substantiallyperpendicular to said images of said heating element on said substratehave a length greater than an expected drifting of images therealongcaused by vibration or tilting of said substrate.
 2. An apparatusaccording to claim 1, wherein an imaging means is disposed between thesubstrate and said at least one first radiation detector.
 3. Anapparatus according to claim 2, wherein said restrictor is disposed inan intermediate image plane of said imaging means.
 4. An apparatusaccording to claim 1, wherein a plurality of said first radiationdetectors are provided, and wherein the fields of vision of said firstradiation detectors are disposed parallel to one another.
 5. Anapparatus according to claim 1, wherein a device for rotating thesubstrate is provided.
 6. An apparatus according to claim 1, wherein atleast one further radiation detector is provided for measuring thermalradiation from at least one heating element.
 7. An apparatus accordingto claim 6, wherein said restricted field of vision of said at least onefirst radiation detector is associated with a field of vision of saidfurther radiation detector.
 8. An apparatus according to claim 1,wherein a plurality of heating elements is provided.
 9. An apparatusaccording to claim 6, wherein said radiation detectors are pyrometers.10. An apparatus according to claim 6, wherein a cylindrical lens isdisposed between the substrate and said radiation detectors.
 11. Anapparatus according to claim 10, wherein said heating elements are rodlamps, and wherein an axis of said cylindrical lens is parallel to axesof said rod lamps.